In integrated circuits, discrete devices such as metal-oxide semiconductor (MOS) transistors are widely used as switching elements. Accordingly, high performance MOS transistors are desired to improve the characteristics of semiconductor devices.
Methods of improving the carrier mobility of transistors by providing a channel stress to a channel region have been researched to obtain a high performance MOS transistors. See, e.g., J. Welser et al “Strain dependence of the performance enhancement in strained-Si n-MOSFETs” IEDM Tech. Dig. 1994, p. 373 and K. Rim et al “Enhanced hole mobilities in surface channel strained-Si p-MOSFETS” IEDM Tech. Dig. 1995, p. 517.
A tensile stress may be provided to a channel region of an NMOS transistor to improve electron mobility. Methods such as implanting carbon ions into source and drain regions of an NMOS transistor or forming a liner layer having a tensile stress on an NMOS transistor may be used to improve the electron mobility of NMOS transistors. In contrast, a compressive stress may be provided to a channel region of a PMOS transistor to improve the hole mobility thereof. Methods such as implanting germanium ions into source and drain regions of a PMOS transistor or forming a liner layer having a compressive stress on a PMOS transistor may be used to improve the hole mobility of PMOS transistors.